1. Field of the Invention
The present invention relates to epoxy-based compositions, particularly well suited for sealing reversibly variable electrochromic devices which are designed to vary the transmittance to light, such as electrochromic rearview mirrors, windows and sun roofs for motor vehicles, and reversibly variable electrochromic elements therefor.
2. Brief Description of the Related Technology Reversibly variable electrochromic devices are known, in which the intensity of light (e.g., visible, infrared, ultraviolet or other distinct or overlapping electromagnetic radiation) is modulated by passing the light through an electrochromic medium. The electrochromic medium is disposed between two conductive electrodes, at least one of which is typically transparent, which causes the medium to undergo reversible electrochemical reactions when potential differences are applied across the two electrodes. Some examples of these devices are described in U.S. Pat. No. 3,280,701 (Donnelly); U.S. Pat. No. 3,451,741 (Manos); U.S. Pat. No. 3,806,229 (Schoot); U.S. Pat. No. 4,712,879 (Lynam); and U.S. Pat. No. 4,902,108 (Byker).
Reversibly variable electrochromic media include those wherein the electrochemical reaction takes place in a solid film or occurs entirely in a liquid solution. Many devices using an electrochromic medium, where the electrochemical reaction takes place entirely in a solution, are known. Some examples are described in U.S. Pat. No. 3,453,038 (Kissa); U.S. Pat. No. 5,073,012 (Lynam); U.S. Pat. No. 5,115,346 (Lynam); U.S. Pat. No. 5,128,799 (Byker); U.S. Pat. No. 5,140,455 (Varaprasad); U.S. Pat. No. 5,142,407 (Varaprasad); U.S. Pat. No. 5,151,816 (Varaprasad); U.S. Pat. No. 5,239,405 (Varaprasad); Manos; and Schoot.
The solution often includes a solvent, an anodic electrochromic compound and a cathodic electrochromic compound. During operation of such devices, the solution is fluid, although it may be gelled or made highly viscous with a thickening agent, and the solution components, including the anodic electrochromic compounds and cathodic electrochromic compounds, do not precipitate. See e.g., Byker.
One problem often encountered with such electrochromic devices is degradation of the sealing element. Degradation may be due to chemical degradation as a result of prolonged contact (particularly during use) with the components of the electrochromic media, which are oftentimes acidic in nature and/or solvents. Degradation may also be caused by environmental exposure, which is common in use.
U.S. Pat. No. 4,761,061 (Nishiyama) speaks to sealing materials such as: thermoplastic resins (e.g., polyethylene, polypropylene, polyester, polystyrene, polyvinyl chloride, ethylene vinyl acetate, ionomer, ethylene ethyl acrylate, polyvinylidene chloride, ethylene acrylate, nylon, polycarbonate, polyethylene fluoride, and the like; thermosetting, photo-curable, or electron-beam-setting resins (e.g., epoxy, silicone, melamine, unsaturated polyester, polyester acrylate, and the like; various inorganic materials (e.g., glass, silica, alumina, titanina, and the like); and mixtures of these materials.
In addition, it is known in the field of cyanoacrylate adhesives to include rubber-toughening agents, such as VAMAC, in the adhesive composition to increase the strength of the cured adhesive product. See U.S. Pat. No. 4,440,910 (O""Connor).
Notwithstanding the above, it would be desirable to provide an epoxy-based composition, such as one for use as a sealing element, that is better able to withstand the chemical rigors to which it will be exposed in use, as well as the environmental weathering that occurs over time in use.
The present invention provides epoxy-based compositions, including an epoxy resin component, at least a portion of which comprises at least two of dicyclopentadiene type epoxy resin, reaction products of 1,6-dihydroxy-napthalene with epichlorohydrin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, and novaloc type epoxy resin, a rubber toughening agent and a latent curing agent. The compositions are extremely well-suited to commercial applications, like sealing elements in the manufacture and use of electrochromic devices. Such electrochromic devices include electrochromic mirrorsxe2x80x94e.g., vehicular, for instance, truck mirrors, particularly large area truck mirrors, automotive interior and exterior mirrors, architectural or specialty mirrors, like those useful in periscopic or dental and medical applications; electrochromic glazingsxe2x80x94e.g., architectural, such as those useful in the home, office or other edifice, aeronautical glazings, such as those useful in aircraft, or vehicular glazings, for instance, windows, such as windshields, side windows and backlights, sun roofs, sun visors or shade bands and optically attenuating contrast filters, such as contrast enhancement filters, suitable for use in connection with cathode ray tube monitors and the like; electrochromic privacy or security partitions; electrochromic solar panels, such as sky lights; electrochromic information displays; electrochromic lenses and eye glass.
The present invention also provides electrochromic devices manufactured using the inventive epoxy-based compositions, such as those referred to above, particularly rearview mirrors, windows and sun roofs for automobiles, which devices possess a sealing element stable to autoclave conditions.